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Circuit Theory and Calculations Flashcards

6 cards from real 309A practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. What is Kirchhoff's Voltage Law (KVL)?

    Answer: The sum of all voltages around a closed loop equals zero

    Kirchhoff's Voltage Law states that the algebraic sum of all voltage drops and rises around any closed loop in a circuit must equal zero, reflecting conservation of energy.

  2. A 10 kW, 240 V single-phase load operates for 8 hours. How many kWh of energy are consumed?

    Answer: 80 kWh

    Energy = Power × Time = 10 kW × 8 hours = 80 kWh. Energy consumption is the product of power and the duration of use.

  3. What is the phase angle between voltage and current in a purely capacitive circuit?

    Answer: 90° (current leads voltage)

    In a purely capacitive circuit, current leads voltage by 90°. This is remembered by the mnemonic 'ICE' — In a Capacitor, current (I) leads voltage (E).

  4. What is the total resistance of four 100 Ω resistors connected in parallel?

    Answer: 25 Ω

    For identical resistors in parallel: Rt = R/n = 100/4 = 25 Ω. The total resistance is always less than the smallest individual resistor.

  5. A transformer has a turns ratio of 10:1. If the primary voltage is 4800 V, what is the secondary voltage?

    Answer: 480 V

    Secondary voltage = Primary voltage / Turns ratio = 4800 / 10 = 480 V. A step-down transformer reduces voltage by the turns ratio.

  6. What is the reactive power in a circuit drawing 20 A at 240 V with a power factor of 0.8 lagging?

    Answer: 2880 VAR

    Apparent power S = 240 × 20 = 4800 VA. Real power P = 4800 × 0.8 = 3840 W. Reactive power Q = √(S² - P²) = √(4800² - 3840²) = √(23,040,000 - 14,745,600) = √8,294,400 = 2880 VAR.